This invention relates to an improved foundry core mix. In a more particular aspect, this invention relates to components of an improved core binder system.
Cores useful in making metal castings are customarily made by placing a foundry aggregate, usually silica sand which has been admixed with a suitable binder, against a shape or pattern and then hardening the binder, as by polymerization. The resulting core is a self-supporting structure which forms a part of a mold assembly.
The cores are made by a variety of processes employing a wide variety of binders. Three well-known processes are the so-called cold box process, no-bake process and the rapid no-bake process. In the cold box process, sand is mixed with a suitable resinous binder composition, blown into a core box, and then gassed with a suitable vapor phase catalyst to cure the binder. By such process, which is described for example in U.S. Pat. No. 3,409,597, a core of sufficient hardness to be stripped from the core box is produced in a matter of seconds.
In the no-bake process, a resinous core binder is mixed with a catalyst and sand and placed in a core box. The core cures at ambient temperatures but much more slowly than in the cold box process, e.g. a period of hours or even days. After a suitable period of time, e.g. two hours, the core can be stripped from the core box, but requires further cure time.
In the rapid no-bake process, which is similar to the no-bake process, the character of the resin and the amount and type of catalyst employed are such that the core can be stripped from the core box in a matter of a few minutes.
There is a continuing need for a binder system which is suitable for use in all three of these processes by adding a suitable catalyst immediately before use. The kind and amount of catalyst employed will be such as to adapt the final binder-sand admixture to the intended purpose. That is, in the cold box process, the catalyst will typically be a gaseous amine, such as triethylamine or dimethylethylamine, dispersed in a suitable carrier such as carbon dioxide. In the no-bake and rapid no-bake processes, tertiary amine catalysts and conventional metal catalysts such as lead naphthenate, dibutyltin dilaurate and others of the same class, are employed in amounts adjusted to provide the desired set time.